Oil-Injected Compressor with Means for Oil Temperature Regulation

ABSTRACT

The invention relates to an oil-injected compressor, in particular, an oil-injected mobile screw compressor with a motor-driven compressor unit, for the generation of compressed air cooperating with an oil circuit for lubrication, the oil tank of which is housed in a subsequent oil separator device for separating the oil from the compressed air. Means for oil temperature regulation are provided, comprising a cooler with a fan. The means for oil temperature regulation comprises a speed variable drive for the fan as adjuster, a regulator device for the speed of the fan matches the heat transferred to the ambient cooling air by the cooler.

BACKGROUND AND SUMMARY

The present disclosure of change relates to an oil-injected compressor, in particular an oil-injected mobile screw compressor, with a motor-driven compressor unit for generating compressed air, with which lubrication interacts with an oil circuit. The oil reservoir accommodated in a downstream oil separator device for separating the oil from the compressed air, means comprising a cooler with fan impeller is provided for regulating the oil temperature.

Besides oil-injected screw compressors, the present means can also be used in other types of oil-injected compressors, such as spiral-type and vane compressors. In compressors of the type in question here, an oil circuit serves to inject lubricating oil into the area of the moving compressor components and at their bearing points. This is to firstly lubricate the roller bearings, here rotating at high speed, and secondly also in order to prevent any inadmissible heating due to friction in the area of the moving compressor components. In addition, the oil also serves to seal off the air side from other areas of the compressor. Owing to their compact dimensions, the sphere of use of such oil-injected compressors extends primarily to mobile applications in rail vehicle construction and also in commercial vehicle construction. In addition, oil-injected compressors are also used in fixed compressed air supply installations.

The general state of the art discloses oil-injected compressors, such as oil-injected screw compressors in different variants. An oil-injected screw compressor basically comprises a compressor unit having at least one pair of contra-rotating and intermeshing, roller-shaped compressor screws. This compressor screw arrangement serves to generate compressed air by continuously compressing atmospheric air drawn in from one side and transforming it into compressed air, which leaves the compressor unit via a spring-returned outlet valve. The compressor screw arrangement is here driven by a flange-mounted motor, generally an electric motor, via a sealed drive shaft led out of the compressor unit. For lubricating, sealing and cooling, the compressor unit subjected to high thermal stresses by the compression process, it is connected to an oil circuit. The oil circuit delivers the oil from an oil reservoir to the compressor screw arrangement and also to the associated roller bearings. The oil injected here leaves this operating area for the oil reservoir, which is situated inside the oil separator device connected downstream of the oil circuit. The oil separator device is needed in order to remove oil from the oil-laden compressed air again, so that oil-free compressed air is available on the outlet side. Usually the oil separator device basically comprises an oil separator, which works on the gravity principle in a manner known in the art. The oil which separates from the oil-laden compressed air rising in the oil separator is collected in the oil reservoir. The compressed air, which is already partially free of oil, and which has risen in the oil separator is then generally fed to a cartridge-type fine separator and then leaves the oil separator device via a pressurizing valve arranged on the outlet side.

For oil-injected compressors to operate reliably a correspondingly high oil temperature is required, especially at high, humid ambient temperatures, in order to prevent the precipitation of condensate with attendant harmful effects inside the compressor. The high oil temperature required is generally rapidly achieved by a control valve arranged in the oil circuit. According to the compressor operating conditions, the control valve continuously regulates and divides the volumetric flow of oil needed for cooling between a cooler line and a bypass line, in such a way that the same oil temperature always prevails. In the state of the art, the fan impeller belonging to the compressor and the oil circuit cooler is operated at maximum power. There is a rigid connection to the drive motor of the compressor unit. Only in separately driven cooler-fan systems is a simple stop-start operation possible, in order to prevent cooling of the oil circuit if the oil temperature is low. The fan, generally permanently operated at rated speed, serves to maintain operation of the compressor unit even in the most unfavorable conditions at high ambient temperatures, so that the maximum admissible oil temperature of 120° C. is not exceeded.

A disadvantage inherent in this state of the art is that designing the fan for maximum demand and maximum air flow means that for most of the time when the compressor unit is in operation the fan is over-dimensioned. Usually this results in an unnecessarily high power demand. In addition, the permanent fan drive gives rise to considerable noise emissions.

The control of the volumetric flow of oil between cooler and bypass line as described above furthermore means that a fixed control temperature prevails in the oil reservoir regardless of the ambient temperature. Since the maximum quantity of water vapor in the ambient air varies substantially as a function of its temperature, the selected oil temperature level must in this case be so high that even under unfavorable conditions no condensate can be precipitated in the compressor. The oil is thereby subject to greater ageing. The same is also true of all rubber and seal parts of the compressor unit, which are exposed to particular stresses due to the constantly high oil temperature. In addition, the oil cannot optimally fulfill its function as gap seal in the actual compressor chamber if it is hot and hence at a lower viscosity, that is to say thinner. Due to internal back flows, the volumetric efficiency declines as the oil temperature increases.

The stop-start mode of operation occurring in mobile applications of the oil-injected compressor and the often lower duty cycle again exacerbates the disadvantage of designing the oil circuit cooling for maximum output with all the disadvantages described above. Owing to the interim cooling effects in the stop phases, the cooling air is then often little needed in operation, if at all, and is sometimes even counter-productive. At extremely low ambient temperatures, the entire fan power from the outset prevents a suitable warming-up of the oil circuit. This leads to a very high hydraulic resistance in the cooler. Thus when the conventional control valve is switched from the bypass line to the cooler line the volumetric flow of oil may collapse and the compressor may sustain damage.

The object of the present disclosure, therefore, is to further improve an oil-injected compressor of the type described above, in such a way that its means of regulating the oil temperature will ensure an efficient cooling commensurate with demand at justifiable engineering cost.

The disclosure encompasses the technical teaching that an adjusting device of a drive for an impeller that regulates the oil temperature comprise a regulating device adjusting the speed of the fan impeller as a function of the heat transmitted to the ambient cooling air by the cooler.

The solution according to the present disclosure is based on the finding that although the warming of the ambient cooling air as it passes through the cooler is approximately constant, the ambient temperature can nevertheless fluctuate markedly. Thus, the final temperature of the cooling air used for cooling is also to a considerable extent dependent on the ambient temperature. The solution according to the disclosure therefore allows two oil temperature control variables to be linked together. Firstly, the oil temperature, which correspondingly heats the cooling air on the cooler, is indirectly inferred as control variable, and secondly, the ambient temperature, which determines the basic level of the cooling air temperature, is also incorporated as control variable. By linking the two control variables in this way, it is also possible to adjust the oil temperature to the prevailing ambient temperature level. In the state of the art, the oil temperature always remains at a constant high level. The solution according to the present disclosure thus allows an operation of the fan impeller that is always adjusted commensurately with the demand. Since the fan impeller has hitherto been operated at maximum output, although this is only necessary for some of the time, considerable improvements result particularly in terms of noise emissions. The overall power demand of the fan impeller is also much less than in the case of a fan impeller permanently operated at the maximum level. The duty cycle also has a considerable influence on the speed of the fan impeller, particularly in mobile use. The heat dissipated in the stop phase of the compressor means that, due to cooling, the compressor on restarting is used at the lowest possible fan impeller speed. This means that even with a low duty cycle the necessary minimum temperature level is swiftly reached, thereby emitting significantly less noise than with the solution disclosed by the state of the art. The solution according to the present disclosure furthermore increases the service intervals for oil and seals. The service life of the compressor bearings is also extended as a result of the adjusted oil temperature.

A viscous drive coupling, which is connected to the constant-speed drive shaft and which varies the slip according to the temperatures prevailing in the operation of the viscous drive coupling, is preferably provided for the variable-speed drive of the fan impeller. The drive shaft of the viscous drive coupling can advantageously be coupled to the shaft of the compressor unit drive motor. This obviates the need for a further drive for this purpose. A conventional viscous drive coupling can be used here, which by means of a simple bimetal, from a specific temperature onwards, discernibly reduces the slip and which due to the oil in the slip area moreover allows the slip to be gently adjusted to the temperature conditions.

Alternatively, it is also possible, however, for the regulating device to adjust the speed of the fan impeller as a function of the heat transmitted to the ambient cooling air by the cooler the heat transmitted may be determined by of a temperature measuring device. In contrast to the variant described above, an electrical temperature sensor with corresponding electronics is required here. The prevailing ambient temperature is registered at a suitable point by the measuring instrumentation. The fan impeller speed is controlled and regulated by means of converters and the fan impeller drive, which may be embodied as a three-phase motor, for example.

Instead of the three-phase motor, however, it is also feasible to use a hydraulic motor, the speed of which can be varied by the admission of hydraulic medium from an upstream hydraulic pump, for the variable-speed drive of the fan impeller. In both cases the control valve for regulating the oil temperature, usual in the state of the art, is dispensed with.

The temperature measuring device or the viscous drive coupling is preferably to be arranged in the flow of cooling air heated by the cooler, between this and the fan impeller. An optimum accommodation in the overall space available is feasible at this point. At the same time the oil temperature, which correspondingly heats the cooling air at the cooler and the influence exerted by the ambient temperature can be indirectly registered at this point and can be converted directly by a temperature sensor or indirectly by a corresponding temperature influencing of the viscous drive coupling into a fan impeller speed regulation commensurate with the demand.

According to a further measure serving to enhance the present diclosure, the cooler, in addition to cooling the oil circuit as described above, can also be used for secondary cooling of the compressed air leaving the oil separator device of the compressor. This obviates the need to provide a separate cooler for this purpose.

Further measures serving to enhance the present disclosure will be described in more detail below together with the description of a preferred exemplary embodiment of the invention, with reference to the single drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE shows a schematic representation of an oil-injected compressor having means for regulating the oil temperature, here incorporating a viscous drive coupling.

DETAILED DESCRIPTION OF THE DRAWINGS

According to the FIGURE an oil-injected compressor (screw compressor) basically comprises a compressor unit 1, which is driven by an electric motor 2. In the area of the compressor screw arrangement forming the compressor unit 1, oil from an oil circuit 3 is injected for the purpose of lubrication. Some of the oil required for lubrication, cooling and sealing purposes here passes into the compressed air leaving the compressor unit 1 on the outlet side. An oil separator device 4 for separating the oil and the compressed air is connected downstream of the compressor unit 1.

The oil separator device 4 contains an oil reservoir 5 for the oil circuit 3. The oil, which the oil separator device 4 separates off from the oil-laden compressed air flowing in, passes into the oil reservoir 5, so that the compressed air flowing off via the compressed air line 6 on the outlet side of the oil separator device 4 is substantially free of oil. The compressed air line 6 is led through a cooler 7 for further cooling of the compressed air. At the same time the cooler 7 also serves for cooling the oil circulating in the oil circuit 3. Via an oil line 8, the heated oil originating from the oil reservoir 5 is fed to the cooler 7 and, correspondingly cooled by the cooler 7, is injected back into the compressor unit 1.

Ambient cooling air is drawn through the cooler 7 by a fan impeller 9, arranged in proximity to the cooler 7. The fan impeller 9 is driven by the electric motor 2 with intermediate viscous drive coupling 10.

In regulating the oil temperature, this arrangement forms a variable-speed drive for the fan impeller 9, which in this respect represents the adjusting device. The regulating device for regulating the oil temperature is embodied by the viscous drive coupling 10, which adjusts the speed of the fan impeller 9 as a function of the heat transmitted to the ambient cooling air by the cooler 7. For this purpose, the viscous drive coupling 10 is arranged in the area 11, which is suitable for registering the ambient air heated by the oil temperature. On the basis of the temperature prevailing in this area 11, the viscous drive coupling 10 varies the slip and hence the speed of the fan impeller 9, which therefore ensures regulation of the oil temperature commensurate with the demand.

The disclosure is not limited to the preferred exemplary embodiment described above, modifications of this being feasible without departing from the scope of the following patent claims. For example, the viscous drive coupling 10 may be replaced by a regulating device of some other type, preferably by an electronic regulating device, which by means of a temperature sensor registers the heat transmitted the ambient cooling air and through automatic control engineering electronically regulates this for a predetermined reference temperature. 

1. An oil-injected compressor comprising: p1 a motor-driven compressor unit for generating compressed air, an oil circuit interacting with the compressor for lubrication and including an oil reservoir and an oil separator device for separating the oil from the compressed air; a cooler for the oil circuit; a fan impeller; a variable-speed drive for the fan impeller; and wherein in the variable speed drive includes a viscous drive coupling in the flow of cooling air heated by the cooler between the cooler and the fan impeller.
 2. The oil-injected compressor as claimed in claim 1, wherein that the variable speed drive adjusts the speed of the fan impeller as a function of the heat transmitted to the ambient cooling air by the cooler, determined by a temperature measuring device, according to a predetermined reference temperature.
 3. The oil-injected compressor as claimed in claim 1 wherein the drive for the fan impeller is embodied as an electric motor.
 4. The oil-injected compressor as claimed in claim 1 wherein the drive for the fan impeller is a hydraulic motor.
 5. The oil-injected compressor as claimed in claim 1, wherein a viscous drive coupling, which is connected to the constant-speed drive and which varies the slip according to the temperatures prevailing in the area of the viscous drive coupling, is provided for the variable-speed drive of the fan impeller.
 6. The oil-injected compressor as claimed in claim 3 wherein the viscous drive coupling is driven via the shaft of the electric motor of the compressor unit. 